1. Field of the Invention
The present invention relates to an electron-emitting device, and also to an electron source substrate, an electron source, a display panel and an image-forming apparatus, using the electron-emitting device. The present invention also relates to methods of producing these devices and apparatus.
2. Related Background Art
In the art of electron-emitting devices, two types are known, one is a thermionic emission source and the other is a cold-cathode emission source. Cold-cathode emission source types include a field emission type (hereafter referred to as an FE type), metal/insulator/metal type (hereafter referred to as an MIM type), and a surface conduction type electron-emitting device.
Examples of FE types are disclosed for example in xe2x80x9cField Emissionxe2x80x9d (W. P. Dyke and W. W. Dolan, Advance in Electron Physics. 8, 89(1956)) and xe2x80x9cPhysical Properties of Thin-Film Field Emission Cathodes with Molybdenum Conesxe2x80x9d (C. A. Spindt, J. Appl. Phys., 47,5248(1976).
An example of an MIM type has been reported by C. M. Mead (J. Appl. Phys., 32,646 (1961)).
An example of a surface conduction type electron-emitting device has been reported by M. I. Elinson (Radio Eng. Electron Phys.,10 (1965)).
Surface conduction type electron-emitting devices use a phenomenon that electron emission occurs when a current is passed through a thin film with a small area formed on a substrate in a direction parallel to the film surface. Various types of surface sconduction electron-emitting devices are known. They include a device using a thin SnO2 film proposed by Elinson et. al., a device using a thin Au film (G. Dittmer, Thin Solid Films, 9, 317 (1972)), a device using a thin In2O3/SnO2 film (M. Hartwell and C. G. Fonstad, IEEE Trans. ED Conf., 519 (1975)), and a device using a thin carbon film (Araki et. al., Vacuum, 26(1), 22 (1983)).
The device proposed by Hartwell is taken here as a representative example of a surface conduction type electron-emitting device, wherein its structure is shown in FIG. 39. In this figure, reference numeral 1 denotes a substrate. Reference numeral 4 denotes an electrically-conductive thin film which is formed of a metal oxide in an H pattern by means of sputtering. The electrically-conductive thin film 4 is subjected to a process called energization forming (hereafter referred to simply as a forming process), which will be described in greater detail later, so that an electron emission region 5 is formed in the electrically-conductive thin film 4. The distance L between electrodes is set to a value in the range from 0.5 mm to 1 mm and the width Wxe2x80x2 is set to 0.1 mm. The detailed position and shape of the electron emission region 5 are not described in the above reference, and thus FIG. 39 is a rough sketch of the structure.
In conventional surface conduction type electron-emitting devices, before using the devices to emit electrons, the electrically-conductive thin film 4 is subjected to an energization forming process thereby forming an electron emission region 5. In this energization forming, a DC voltage or a voltage which rises at a very slow rate for example 1 V/min is applied across the electrically-conductive thin film 4 so that the electrically-conductive thin film is locally broken, deformed, or changed in quality, thereby forming an electron emission region 5 having a high electric resistance. In the electron emission region 5, cracks are partially formed in the electrically-conductive thin film 4 and electrons are emitted via the cracks or via regions near the cracks. After completion of the forming process, a voltage is applied across the electrically-conductive thin film 4 so that a current flows through the electrically-conductive thin film 4 thereby emitting an electron from the electron emission region 5.
The electron-emitting device of the surface conduction type has a simple structure and thus can be easily produced. Therefore, it is possible to dispose a great number of similar devices over a large area. To take such advantages in practical applications such as an electron beam source, a display device or an image display device, etc., extensive research and development is being done.
The inventors of the present invention have investigated the electron-emitting device of the surface conduction type and have proposed a new method of producing an electron-emitting device in Japanese Patent Application Laid-Open No. 2-56822 (1990). FIG. 38 shows the device disclosed in this patent. In this figure, reference numeral 1 denotes a substrate, reference numerals 2 and 3 denote a device electrode, reference numeral 4 denote an electrically-conductive thin film, and reference numeral 5 denotes an electron emission region. This electron-emitting device can be produced as follows. First, device electrodes 2 and 3 are formed on a substrate 1 using a common technique such as vacuum evaporation and photolithography. Then an electrically conductive material is coated on the substrate by means of for example dispersive coating and then is patterned so as to form an electrically-conductive thin film 4. A forming process is then performed by applying a voltage across the device electrodes 2 and 3 thereby forming an electron emission region 5.
However, in the conventional production method described above, it is based on the semiconductor process and thus it is difficult to form a large number of electron-emitting devices over a large area. Besides, this technique needs a special and expensive production apparatus. Furthermore, the above patterning process requires a plurality of long steps. At present, therefore, high cost is required to form a great number of electron-emitting devices over a large area of a substrate. Thus there is a need for a simplified patterning technique.
It is an object of the present invention to solve the above problems. More particularly, it is an object of the present invention to provide a method of producing an electron-emitting device, capable of forming a large number of electron-emitting devices on a substrate at a low cost. It is another object of the present invention to provide an electron source substrate, an electron source, a display panel, and an image-forming apparatus using such an electron-emitting device.
It is still another object of the present invention to provide a method of producing an electron-emitting device, in which patterning is performed with a simplified process.
It is a further object of the present invention to provide a method of producing an electron-emitting device, capable of supplying a desired amount of conductive material at a desired location on a substrate, using a simplified production process.
It is still another object of the present invention to provide an electron source substrate, an electron source, a display panel, and an image-forming apparatus using such an electron-emitting device.
The above objects are achieved by the present invention having various aspects and features as described below.
In a first aspect of the present invention, there is provided a method of producing an electron-emitting device including the steps of: forming a pair of electrodes and an electrically-conductive thin film on a substrate in such a manner that the pair of electrodes are in contact with the electrically-conductive thin film; and forming an electron emission region using the electrically-conductive thin film, the method being characterized in that a solution containing a metal element is supplied in a droplet form onto the substrate thereby forming the electrically-conductive thin film.
In a second aspect of the present invention, there is provided a method of producing an electron-emitting device having a thin film forming an electron emission region between a pair of (each pair of) electrodes located at opposing positions on a substrate, the method including the steps of: supplying one or more droplets of solution onto the substrate, the solution including a material constituting the electrically-conductive thin film; detecting the state of the supplied droplets; supplying one or more droplets again on the basis of the obtained information of the state of the supplied droplets.
In a third aspect of the present invention, there is provided a method of producing an electron-emitting device, including the steps of: forming an electrically-conductive thin film by supplying a plurality of droplets so that the center-to-center distance between adjacent dots formed by the droplets is less than the diameter of the dot; and passing a current through the electrically-conductive thin film so that an electron emission region is formed in each electrically-conductive thin film.
In a fourth aspect of the present invention, there is provided a method of producing an electron-emitting device, including the steps of: treating the surface of the substrate so that the surface of the substrate becomes hydrophobic; and then supplying a solution in a droplet form containing a material constituting an electrically-conductive thin film to a location between a pair of electrodes thereby forming an electrically-conductive thin film, the above solution being hydrophilic.
In a fifth aspect of the present invention, there is provided a method of producing an electron-emitting device, including the steps of: supplying at least one droplet of solution onto a substrate, the solution including a material constituting an electrically-conductive thin film, thereby forming an electrically-conductive thin film in a dot shape; and then forming a pair of device electrodes in such a manner that the device electrodes are in contact with the electrically-conductive thin film.
It should be understood that an electron-emitting device produced according to the production method of the invention is also included in the scope of the invention.
The present invention also provides an electron source substrate characterized in that a plurality of electron-emitting devices according to the present invention are disposed on a substrate.
The present invention also provides an electron source characterized in that a plurality of electron-emitting devices on the electron source substrate of the invention are connected.
Furthermore, the present invention provides a display panel comprising: a rear plate provided with the electron source of the invention; and a face plate provided with a fluorescent film, the rear plate and the face plate being located at opposing positions, whereby the fluorescent film is irradiated by an electron emitted by the electron source thereby displaying an image.
The present invention also provides an image-forming apparatus including the display panel of the invention and further at least a driving circuit connected to the display panel.
The present invention also provides an apparatus for producing an electron-emitting device.
In one aspect of the invention, there is provided an apparatus for producing an electron-emitting device, the apparatus comprising: droplet supplying means for ejecting a droplet containing a metal element toward a substrate thereby supplying the droplet on the substrate; detection means for detecting the state of the supplied droplet; and control means for controlling the ejecting condition of the droplet supplying means on the basis of the information obtained via the detection means.
In another aspect of the invention, there is provided a method of producing an electron source substrate, including the steps of: forming a plurality of pairs of device electrodes on a substrate; and supplying one or more droplets of a solution containing a metal element onto a location between each pair of device electrodes thereby forming an electrically-conductive thin film at that location and thus forming a plurality of electron-emitting devices.
In still another aspect of the invention, there is provided a method of producing an electron source, including the steps of: forming a plurality of pairs of device electrodes on a substrate; supplying one or more droplets of a solution containing a metal element onto a location between each pair of device electrodes thereby forming an electrically-conductive thin film at that location and thus forming a plurality of electron-emitting devices; and connecting the electron-emitting devices via interconnections.
In a further aspect of the invention, there is provided a method of producing a display panel, including the steps of: forming a plurality of pairs of device electrodes on a substrate; supplying one or more droplets of a solution containing a metal element onto a location between each pair of device electrodes thereby forming an electrically-conductive thin film at that location and thus forming a plurality of electron-emitting devices; connecting the electron-emitting devices via interconnections; and connecting a rear plate, having the substrate on which electron-emitting devices are formed, to a face plate provided with a fluorescent film via a supporting frame so that both plates are located at opposing positions.
In still another aspect of the invention, there is provided a method of producing an image-forming apparatus, including the steps of: forming a plurality of pairs of device electrodes on a substrate; supplying one or more droplets of a solution containing a metal element onto a location between each pair of device electrodes thereby forming an electrically-conductive thin film at that location and thus forming a plurality of electron-emitting devices; connecting the electron-emitting devices via interconnections; connecting a rear plate, having the substrate on which electron-emitting devices are formed, to a face plate provided with a fluorescent film via a supporting frame so that both plates are located at opposing positions thereby forming a display panel; and connecting a driving circuit to the display panel.
In the method of producing an electron-emitting device according to the present invention, since a solution containing a metal element is supplied in a droplet form onto a substrate thereby forming an electrically-conductive thin film which constitutes an electron emission region, it is possible to supply a desired amount of solution at a desired location. Thus, it is possible to greatly simplify the process of producing an electron-emitting device.
Furthermore, in the second aspect of the invention regarding the method of producing an electron-emitting device, information of the sate of a supplied droplet is detected, then the ejecting conditions and the ejecting position are corrected on the basis of the obtained information, and finally a droplet is supplied again under the corrected conditions. Therefore, it is possible to produce a thin film having a very small number of defects. Furthermore, it is possible to achieve a great improvement in uniformity of device characteristics, and thus it is possible to solve the problem of the production yield which becomes serious with the increase in the size of the substrate.
Furthermore, it is possible to produce a high-quality electron source substrate, electron source, display panel, and image-forming apparatus, using the electron-emitting device of the invention.
In the third aspect of the present invention regarding the method of producing an electron-emitting device, a plurality of droplets of a solution in which a metal material which constitutes an electron emission region is dissolved or dispersed are supplied onto a substrate so that the center-to-center distance between adjacent dots formed by the droplets is less than the diameter of the dot. Thus, it is possible to form the electrically-conductive film constituting the electron emission region with very high accuracy.
In the fourth aspect of the present invention concerning the method of producing an electron-emitting device, the surface of the substrate is treated so that the surface of the substrate becomes hydrophobic, and then a hydrophilic solution in a droplet form is supplied onto a substrate. Thus, it is possible to produce an electrically-conductive thin film with good reproducibility. This means that it is possible to produce a great number of surface conduction electron-emitting devices having uniform characteristics over a large area.
Furthermore, in the fifth aspect of the invention regarding the method of producing an electron-emitting device, device electrodes are formed after forming an electrically-conductive thin film. This allows the present invention to be used in a wider range of applications.
Furthermore, in the production of an electron source, an electron source substrate, a display panel, an image-forming apparatus, and an electron-emitting device according to the present invention, an electrically-conductive thin film can be disposed precisely at a desired location, and thus it is possible to achieve uniform and excellent characteristics.